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Graphene nanoelectronics from ab initio theory

Graphene nanoelectronics from ab initio theory. Jesse Maassen , Wei Ji and Hong Guo Department of Physics, McGill University, Montreal, Canada. Motivation (of studying a graphene/metal contact).

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Graphene nanoelectronics from ab initio theory

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  1. Graphene nanoelectronics from ab initio theory Jesse Maassen, Wei Ji and Hong Guo Department of Physics, McGill University, Montreal, Canada APS -- March Meeting 2011

  2. Motivation(of studying a graphene/metal contact) • Graphene has interesting properties (i.e., 2D material, zero gap, linear dispersion bands, …). • For electronics, all graphene sheets must unavoidably be electrically contacted to a metal (source/drain). • Can the graphene/metal interface largely influence the global response of the device? • Subject of much experimental and theoretical research. APS -- March Meeting 2011

  3. Motivation(of studying a graphene/metal contact) • Experimental works: Nature Nanotechnology 3, 486 (2008) Phys. Rev. B 79, 245430 (2009) Photocurrent experiments APS -- March Meeting 2011

  4. Motivation(of studying a graphene/metal contact) • Experimental works: Nature Nanotechnology 3, 486 (2008) Phys. Rev. B 79, 245430 (2009) Photocurrent experiments APS -- March Meeting 2011

  5. Our goal Parameter-free transport calculation of a graphene / metal interface APS -- March Meeting 2011

  6. DFT + Simulation Box  HKS Left lead Right lead System NEGF + - - Theoretical method • Density functional theory (DFT) combined with nonequilibrium Green’s functions (NEGF)1 • Two-probe geometry under finite bias APS -- March Meeting 2011 1Jeremy Taylor, Hong Guo and Jian Wang, PRB 63, 245407 (2001).

  7. Metal Atomic structure • Which metals? What configuration at the interface? • Cu, Ni and Co (111) have in-place lattice constants that almost match that of graphene (PRL 101, 26803 (2008)). • Found most stable configuration (1stC on metal, 2ndC on hollow site). After relaxation APS -- March Meeting 2011

  8. Metal Graphene-metal interface Bandstructure of hybrid graphene | Cu(111) system • Graphene states in black • Weak hybridization • n-type graphene Appl. Phys. Lett. 97, 142105 (2010) APS -- March Meeting 2011

  9. Graphene-metal interface Transport properties: graphene | Cu(111) junction • Double minimum T. • T almost perfectly described by pure graphene at TMIN. Appl. Phys. Lett. 97, 142105 (2010) APS -- March Meeting 2011

  10. k E EF Graphene-metal interface Transport properties: graphene | Cu(111) E = 0.2 eV Transmission • Momentum filtering k Nano. Lett. 11, 151 (2011) kz kx APS -- March Meeting 2011

  11. Graphene-metal interface Transport properties: graphene | Cu(111) junction • One Dirac point pinned, while other moves with V. • Peak in conductance  doping level of graphene Appl. Phys. Lett. 97, 142105 (2010) APS -- March Meeting 2011

  12. : A-site C(pz) : B-site C(pz) : Ni(dZ2) Graphene-metal interface Band structure : graphene-Ni(111) system • Strong hybridization with metal • No more linear bands • Spin-dependent band gaps Nano. Lett. 11, 151 (2011) APS -- March Meeting 2011

  13. Graphene-metal interface Transport properties : graphene-Ni(111) system APS -- March Meeting 2011 Nano. Lett. 11, 151 (2011)

  14. Graphene-metal interface Transport properties : graphene-Ni(111) system APS -- March Meeting 2011 Nano. Lett. 11, 151 (2011)

  15. Graphene-metal interface Transport properties : graphene-Ni(111) system • Spin-dependent band gaps  large spin filtering Nano. Lett. 11, 151 (2011) APS -- March Meeting 2011

  16. Graphene-metal interface SUMMARY • Performed a parameter-free calculation of electronic transport through a graphene/metal interface. • Cu merely n-dopes the graphene resulting in: • Double T minimum • Similar trends for Al, Ag, Au & Pt • Simple modeling • Ni & Co create spin-dependent (pseudo-) band gaps in graphene.  Large spin injection efficiencies ~80%. APS -- March Meeting 2011

  17. Thank you ! Questions? Financial support: NSERC, FQRNT and CIFAR Computation facilities: RQCHP APS -- March Meeting 2011

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